After almost two years of bargaining, unionized postdoctoral researchers at the University of Massachusetts Amherst overwhelmingly ratified a contract Thursday that sets a minimum salary of $38,500, provides a 2 percent raise, and guarantees health insurance and other benefits for family members.

The contract, which affects more than 200 researchers, is the firstof its kind in the UMass system. It sets a precedent for the Boston and Dartmouth campuses, where smaller numbers of postdoctoral researchers have unionized and are now likely to begin negotiations themselves, said union spokesman Roger Kerson.

The UMass contract could also have a ripple effect at other universities, since the agreement is one of few in existence, said Gary Rhoades, a professor of higher education at the University of Arizona. “I think this is the wave of the future. People are watching what happens at Amherst.’’

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The researchers occupy an uncomfortable middle ground in academia. Although they are university employees, they are still technically in training, and their positions typically last only a few years.

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Most are not unionized. Efforts to form a union in the California state system intensified in the early 2000s, but did not succeed until 2008, partly due to concerns about straining the researchers’ relationships with their faculty mentors and partly due to student criticism of union practices.

At UMass, the researchers were the only employees who were not unionized before the formation in 2010 of the current group, which is affiliated with the United Auto Workers.

Most such employees work in the sciences, although in the last few years they have become increasingly prevalent in the humanities.

There is no official nationwide tally, but some estimates put the number as high as 90,000. That represents a tripling over the past three decades as students have flocked to doctoral programs, with no concomitant increase in the number of tenure-track faculty positions, and as universities have come to rely on postdoctoral employees for inexpensive labor.

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It is increasingly common for doctorate holders to get stuck in a sort of academic purgatory, cycling through two or three postdoctoral positions before winning tenure-track jobs.

“There’s kind of a personal window on how long one can be a postdoc before giving up the dream,’’ said Christopher Varney, a UMass Amherst theoretical physics researcher who is on his second postdoctoral position. “I know one person who did eight years of postdocs before getting a faculty job. He was 38.’’

Some employees, especially those in biomedical sciences, benefit from salary minimums set by organizations such as the National Institutes of Health.

But all have their pay determined by the grace of their faculty advisers, who supply it from grant funding, “so the amounts are kind of all over the place,’’ said Sarah Conte, a UMass Amherst postdoctoral researcher who studies plant biology.

At Amherst, Conte added, “there are people on campus right now who are being paid $32,000 after getting a PhD, and a lot of them have families. So this agreement is huge for us. It’s a lot more livable.’’

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Under the new contract, even the greenest postdoctoral researchers at UMass Amherst will make at least $38,500 starting Sept. 1. (Until then, the floor will be $37,500.) Those at the low end of the salary scale will also be partly reimbursed for child-care expenses. Researchers with more experience will have higher salary minimums, up to $47,000.

At UMass Amherst, they will also qualify for health insurance that covers family members. Dental and vision insurance will be available for free, and to their families for a small fee.

The bargaining that went into the new UMass Amherst contract was surprisingly complicated, said James Staros, the school’s provost. “There were a number of issues. One was, ‘Who’s a postdoc?’ That’s a very different definition from place to place, and it took a lot of sorting out,’’ he said.

The end result could be good for the employees, the university, and perhaps American science as a whole, said Rhoades, who observed unionization from the front lines as a recent general secretary of the American Association of University Professors.

Many postdoctoral employees in the United States are from India and China. Those countries are investing heavily in researchers, Rhoades said, and could gain an edge in attracting talent if their salaries outstrip those of American institutions.

“In the long run, it’s a bad idea to try to produce science on the cheap,’’ he said. “What we’re seeing now is a pattern: First, the recognition that the plight of postdocs is a problem, and second, that collective bargaining is going to be fundamentally important.’’